Its simple, the lead car ALWAYS has the right of way. Should the 2 be cars wheel to wheel batteling for position, the inside car would have the right of way.
That being said I would suggest never trying to pass a backmarker in this situation since someone slow enough to be that far behind you is unlikely to have enough command of his car to complete the section without striking your car. It is also advisable to yeild the turn while in the lead when you feel the other driver is likely to collide with you. Its better to give it up and work to get it back than get punted off and lose your postion, time and possibly parts.